Study On In-situ Synthesis Of ZrB₂-ZrC Reinforced Ni-based Composite Coating By Plasma Cladding

The service life of parts can be greatly improved by using surface strengthening technology to cladding a coating with high hardness and wear resistance on the surface of parts.In this paper,two kinds of composite coatings of ZrB2-ZrC/Ni and ZrB2-ZrC-SiC/Ni were synthesized by plasma transfer arc cladding on Q235 steel substrate with Ni powder,Zr powder,B4C powder and SiC powder as raw materials.The phase composition and microstructure of the cladding layer were analyzed by X-ray diffraction(XRD),electron probe micro-analyzer(EPMA),energy dispersive spectrometer(EDS),respectively.The microhardness and wear resistance of the cladding layer were tested by microhardness tester and multifunctional friction and wear tester,respectively.The results showed that ZrB2-ZrC reinforced Ni-based composite coatings were successfully prepared on Q235 substrate by plasma transfer arc cladding.There was a sound metallurgical bonding between the coating and the substrate.The cladding layer is fully compact and free of cracks.Nevertheless,it can be seen that there were some pores in the coating.The main constituents of the coatings are ZrB2 and ZrC phases.The ZrB2 particles present the needle-like and rod-like structure,while the ZrC particles exhibit the granular structure.The microstructure of the coatings with SiC addition was refined significantly.And the acicular shaped phase was obviously refined with 20 wt.%SiC addition(SiC addition amounts were 0,10,15 and 20 wt.%,respectively).Due to the presence of reinforced phases,the microhardness and wear resistance of the coatings were significantly higher than that of the Q235 substrate.The hardness and wear resistance of ZrB2-ZrC/Ni composite coating is 5-7 times and 15 times that of Q235 steel,respectively.With the addition of SiC,the microhardness and wear resistance of the composite coatings were further improved.Compared with the coating with no SiC addition,the microhardness and wear resistance for coatings with 20 wt.%SiC addition increased by about 17%and 65%.The worn surface of the coatings were relatively smooth in spite of some shallow grooves and spalling pits,indicating that the dominant wear mechanism of the coatings was fatigue wear.